`Bài 1 : x^2 - 11x + 28 `
` ⇔ ( x^2 - 7x ) - ( 4x + 28 )`
` ⇔ x ( x - 7 ) - 4 ( x - 7 ) `
` ⇔ ( x - 4 ) ( x - 7 ) `
`x^2 - ( a + b )x + a*b`
`Bài 2 : 6(x^2) + x - 12 `
` ⇔ ( 6(x^2) + 9x ) - ( 8x + 12 ) `
` ⇔ 3x ( 2x + 3 ) - 4 ( 2x + 3 )`
` ⇔ ( 2x + 3 ) ( 3x - 4 )`
` a(x^2) + b^2 + c`
Tách b = m + n | Đ/K ` ac = mn`
` Bài 3 : x^3 - 19x + 30 `
` ⇔ ( x^3 - 4x ) - ( 15x + 30 ) `
` ⇔ x ( x - 2 ) ( x + 2 ) - 15 ( x - 2 ) `
` ⇔ ( x - 2 ) [ x ( x + 2 ) - 15 ]`
` ⇔ ( x - 2 ) [ x^2 + 5x - 3x - 15 ]
` ⇔ ( x - 2 ) ( x + 3 ) ( x + 5 ) `
` x^3 - ( a^2 + b )x - ab `
` color(blue){ # KAITO # } `
